Typical microelectronic systems have various electronic components that often share one or more common biasing circuits. Examples of circuits that have common biasing arrangements include current sources, operational amplifiers, comparators, as well as other various analog and digital functions. The various circuit functions operate in a predictable fashion when the biasing circuits reach steady-state operation. However, stable operation of the various circuit functions can be delayed as a result of start-up transients and other conditions that occur when power is initially applied to the circuit. In digital circuits, it is possible that a digital logic circuit may find a trapped state or other undetermined condition during power-up. Similarly, analog circuits may reach a condition where transistors lock themselves in an off condition during power.
Various power-on detector circuits are used in electronic systems to ensure that a stable operating power-up condition has been achieved. Start-up circuits and power-on reset (POR) circuits can be used to initialize circuits and otherwise stabilize the operating conditions of various circuits. A POR signal is often asserted during an initial power-up sequence until some minimal operational criteria is achieved. Logic initialization problems can be avoided by incorporating reset circuits that are held active while a POR signal is asserted. Also, one or more nodes in various circuits can be initialized to a desired operation condition while the POR signal is asserted. Once the POR signal changes states, the various circuit functions can be presumed to be operating in a predictable fashion.